1. Field of the Invention
The present invention relates to transmission devices for vehicles, and in particular for front wheel drive vehicles.
2. Description of the Prior Art
The recent evolution of such transmissions leads to the contemplation of different types of configurations.
First of all, when the engine is disposed transversely relative to the longitudinal axis of the vehicle, one has been led, in order to be able to use two short transmission shafts of equal length, to provide at the output of the differential integrated in the motor-drive unit, a relay shaft located on the side of the differential remote from the associated driving wheel, this relay shaft being supported by an intermediate bearing. This solution is not satisfactory, since the placement of the intermediate bearing is not always easy and the assemby is consequently complicated.
There may also be provided an option consisting in incorporating in the differential a control or locking device. The control device may be a coupling having a limited slip, such as that known for example under the trade mark VISCODRIVE. The drawback of such a solution resides mainly in the fact that the part of the case containing the gear box and the differential must be modified, which of course complicates the manufacturing operations and increases the cost.
It has also been envisaged to integrated homokinetic joints in differentials, but this arrangement presents three essential drawbacks.
First, an assembly constituted by the gear box and one or two pre-mounted transmission shafts is space-consuming and therefore difficult to transport. Furthermore, such an arrangement is relatively fragile.
Second, as the sealing of the gear box is ensured not only by rotating seals but also by the rubber bellows of the joints, a deterioration of these bellows may result in a loss of oil of the gear box and possibly its deterioration.
Third, the replacement of a bellows or of a transmission shaft involves considerable dismantling.